This proposal aims to investigate the mechanical properties of irradiated metallic fuels with nano-indentation to support modeling capabilities for fuel cladding mechanical interaction (FCMI). U-10Zr fuel has a very complex microstructure made of a heterogeneous mixture of multiple phases. Fuel microstructure and chemistry is further complicated by irradiation and temperature gradients experienced in a reactor environment, which causes elemental redistribution and phase changes. The proposed project will investigate the mechanical properties of irradiated fuel by performing nano-indentation on an irradiated U10Zr fuel sample to determine the hardness and elastic modulus of its component phases. This project will require access to NSUF facilities at the Materials Fuel Complex (MFC) in the Irradiated Materials Characterization Laboratory (IMCL). The experimental plan will use shielded Plasma Focused Ion Beam (PFIB) to prepare cube shaped lift-outs from an irradiated U-10Zr sample. The lift-outs will then be subjected to nanoindentation with the Hysitron/BrukerPI88 nano indenter to determine hardness and elastic modulus of key phases in the U10Zr sample. After indentation the sample will be brought to the G4 Helios PFIB where the ion beam will be used to cut consecutive slices to generate a 3D reconstruction of the lift out cube. This technique involves software that implements an iterative slice-and-view process.

This proposal supports the DOE-NE mission by improving the materials science understanding of metallic fuels that have been explored for advanced reactor concepts. The mechanical properties of metallic fuels have a major impact on the stress profile within the fuel and on the maximum stress subjected on the cladding. Because of this impact on fuel cladding mechanical interactions (FCMI) measuring the mechanical properties of irradiated metallic fuels is an important step in licensing. This study will perform nano-indentation on the individual phases of an irradiated U10Zr fuel sample (ID:MNT54C). The collection of this data will allow for the calculation of hardness and elastic modulus of the major phases in irradiated U10Zr. This data would be valuable for improving FCMI models and beneficial to the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program. The data would also be relevant to understand the complex behavior of nuclear fuel under irradiation and transient conditions, which could be of interest to the Advanced Fuel Campaign (AFC).